The separation of peptides and other biologically active species is of great importance in the elucidation of their structure and function. High pressure liquid chromatography is just beginning to be employed routinely for the separation of such compounds. This proposal describes two systems, one for the separation of peptides and one for the separation of nucleotides and nucleosides. For the separation of peptides the chromatographic column is packed with silica gel to which a peptide stationary phase is bonded. These bonded phases seem to be able to separate peptides which are structurally similar. By changing the nature of the bonded peptide we can alter the resolving power of the chromatographic column. For the separation of nucleotides and nucleosides, we are attempting to use metal ions in either the stationary phase or mobile phase. The formation of complexes between the metal ions and the nucleotides controls the retention behavior of the solutes and excellent separations of nucleotides can be achieved isocratically. By changing the amount of the metal ions, the separation of nucleotides and nucleosides can be optimized.